Here we go again.
1. Price. Just pay whatever you think it's worth. You just need to tell them what they're going to accept. That's how it works, isn't it? I have heard that some people shop around and compare prices but I'm not convinced anyone actually does. Sounds too far fetched.
2. Insurance. Tell them that if they expect to get your business they'll have to charge you the same as an older, more experienced rider. No point trying anywhere else because every insurance company offers exactly the same product and prices.
3. Comfort. You'll have to live with it the way it is. I don't think anyone's ever even considered changing the seat or peg position on a Rocket. You're the first! Well done. I would imagine the way you'd go about it would be to maybe try one out and, I don't know, see how you like it. Now this is real greenfields stuff but maybe if it wasn't quite the way you wanted things you could then look around at options for changing it a little to better suit YOU.
4. Sound. The Rocket is the only bike ever made that cannot be made louder. There are no exhaust modifications possible. Sorry, but that's the way it is.